This paper describes the design of a deep-UV Raman imaging spectrometer operating with an excitation wavelength
of 228 nm. The designed system will provide the ability to detect explosives (both traditional military explosives
and home-made explosives) from standoff distances of 1-10 meters with an interrogation area of 1 mm x 1 mm to
200 mm x 200 mm. This excitation wavelength provides resonant enhancement of many common explosives, no
background fluorescence, and an enhanced cross-section due to the inverse wavelength scaling of Raman scattering.
A coded-aperture spectrograph combined with compressive imaging algorithms will allow for wide-area
interrogation with fast acquisition rates. Coded-aperture spectral imaging exploits the compressibility of
hyperspectral data-cubes to greatly reduce the amount of acquired data needed to interrogate an area. The resultant
systems are able to cover wider areas much faster than traditional push-broom and tunable filter systems. The full
system design will be presented along with initial data from the instrument. Estimates for area scanning rates and
chemical sensitivity will be presented. The system components include a solid-state deep-UV laser operating at 228
nm, a spectrograph consisting of well-corrected refractive imaging optics and a reflective grating, an intensified
solar-blind CCD camera, and a high-efficiency collection optic.
This paper describes the application of a coded aperture snapshot spectral imager (CASSI) to fluorescence microscopy. CASSI records an interleaved spatially varying, spectrally filtered map of an object on a 2D focal plane. Convex optimization techniques combining least squares QR factorization with a total variance constraint are used to reconstruct a 3D data cube from a spectrally encoded 2D scene. CASSI records a 3D dataset at video rate - making it suitable for dynamic cellular imaging. We report on the reconstruction of fluorescent microspheres used in fluorescence microscopy applications and compare the results with images from a multi-spectral confocal system.
We have designed and constructed a multimodal multiplex Raman spectrometer which uses multi-wavelength excitation to better detect signals in the presence of fluorescence by taking advantage of the shift-variance of the Raman signal with respect to excitation frequency. Coupled with partial-least-squares (PLS) regression, the
technique applied to ethanol estimation in a tissue phantom achieves root-mean-squared-cross-validation errors (RMSCVE) of 9.2 mmol/L with a model formed with 2 principal components, compared to a single wavelength data set with equivalent energy where 7 principal components were used to achieve an RMSCVE of 39.1 mmol/L.
Optical diagnostics in biological materials are hindered by fluorescence and scattering. We have developed a multimodal, multiplex, coded-aperture Raman spectrometer to detect alcohol in a lipid tissue phantom solution.
We have developed a class of aperture coding schemes for Remote
Raman Spectrometers (RRS) that remove the traditional trade-off
between throughput and spectral resolution. As a result, the size
of the remote interrogation region can be driven by operational,
rather than optical considerations. We present theoretical
arguments on the performance of these codes and present data from
where we have utilized these codes in other spectroscopy efforts.